In recent years there have been developed, particularly for oil field or oil well drilling applications, improved, high speed, high pressure, single acting pumps, or slush pumps.
These new pumps run up to, or operate as fast as, 200 revolutions per minute, or more, which means or requires that the valves of these pumps must be capable of cycling, or opening and closing, more than three times a second.
The new pumps also operate under extremely high fluid pressures in the heighborhood of 5,500 pounds per square inch (5,500 PSI) or more. At that pressure the overall load on top of a typical, say 4 in. I.D. valve, having a complete top area of two times the cross-sectional area of its seat, would be 100,000 pounds (100,000 lbs.).
The extreme high speed and pressure conditions of the new single acting pumps have introduced or brought with them a variety of new problems relating to the seals and sealing of, and to the wear or life of, the pump valves.
One problem with the new pumps arises from their very rapid operation, at better than three cycles per second, and whereby the pump valves can in continuous operation experience or undergo as many as a million closings in only about a month's time.
The problems created by the described continuous, high speed, high pressure valve cycling are those of rapid and excessive wear of the valve body and seat faces; of like wear of the valve seals; and of the latter compounding the former.
The conventional or prior valves, that have been attempted to be employed with the new pumps, are generally understood, then, to be subject to excessive or too rapid wear at the metal faces of both the valve body and the valve seat.
Thus it has been recognized as well that, by the overcoming or elimination of the metal wear problem, the operating or useful life of the valves could be significantly extended.
Such valves life extending is, of course, of the utmost significance, or economic benefit.
That benefit is measured in part by the significant reduction to be achieved in the very costly down-time or shutdown of the pumps for the valve repair, and in further part by the very large savings to be made in the substantial labor and material expense of the wear-necessitated change or replacement both of the valve body and of the valve seat.
Applicant has found that the solution to the foregoing problem lies in the adequate provision by the valve seal of each or both of the double functions of cushioning and of sealing the valve closings. As to the cushioning, it has been determined more particularly that the valves here concerned need or require to be significantly slowed in the final, say 1/16 in. of their travel to or descent against the valve seat.
Only by the adequate cushioning can the excessive wear of the valve body and seat faces by the very rapidly repeated, high impact, valve-to-seat engagement, and the described attendant problems of pump maintenance and service interruption, be successfully prevented or guarded against.
Applicant has analyzed the problem of cushioning the high speed, high pressure slush pumps, and from that discovered that the following six conditions must be met, to enable the requisite adequate cushioning to be supplied:
1. The seal must be conical, must be a paralleling, contiguous, upstream extension of the valve body seating face, and must have full, flat seating engagement against a like-tapered conical seating face of a valve seat that extends both outwardly of the seal and inwardly to fully oppose also the valve body seating face.
2. There must be a sufficient, but not excessive, overhang of the seal, or extending of it outwardly of or below the metal seating face or surface of the valve body.
3. The valve seat face, the seal-backing valve body groove face, and the overhanging valve seal face must all parallel each other, whereby the valve seal is uniformly compressed throughout its cross-section in the course of the valve closing.
4. There must be rigid back-up of the valve seal by the valve body during the course of the valve seal compressing by the valve closing, this without any upward deflection of the valve body during the valve closing, and whereby the compressive impact of said closing is initially taken up or absorbed wholly by, and therefore is fully resisted by, the valve seal.
5. The valve body groove must be sufficiently wider than the valve seal to accommodate therewithin the valve seal volume that is displaced from the seal overhang upon the seal's compression to within the plane of the valve body seating face.
6. In order to return to its full normal or uncompressed shape or depth within the very brief time interval between successive valve closings, the valve seal must have an elastic return or shape recovery rate which is higher or faster than that characteristic of or normally attainable with the rubber or rubberous materials that are suitable therefor.
The valve seal and valve body constructions and arrangements of the prior art that have heretofore been tried with the new high speed, high pressure slush pumps have failed to solve the problem, and more particularly have not supplied in combination the foregoing requirements that applicant has discovered to be necessary.
The seals of certain prior art valves have been backed by a relatively thin plate on top of the seal. Such thin plate is found to have deflected under the valve closing impact, and to have thereby prevented the required cushioning or slowing down of the final 1/16 in., or thereabouts, of the valve's descent, through its yielding to, and non-rigid backing of the seal against and for proper compression under, the closing impact.
Applicant has also found, as above noted, that the normal resiliency or elasticity of the rubber or rubberous seal materials will not allow or afford full elastic recovery, or return to full extended shape, rapidly enough for these modern pumps, or within the 1/3 second or less time interval between their successive valve closings.
In certain prior art valves, again, the valve seat face, valve-seal-backing groove face, and intervening valve seal face have not been parallel. The valve seal hence has not been of uniform cross-section, and the seal has therefore not been uniformly compressed throughout its length and width in the valve closing, and with the result that there has not been the requisite or maximum cushioning by, and for or within the necessarily limited protrusion of, the seal.
This invention novelly solves the foregoing cushioning problem, and more particularly fully satisfies all the above enumerated requirements thereof.
The second operative requirement of the high speed, high pressure slush pump valve seals, namely, that of sealing the pump valves, represents yet another unsolved problem of the special sealing application here concerned.
The problem is that, At the initial instant of valve closing, seal-to-seat contact, before the seal has been compressed to where come into contact also the metal valve body and seat surfaces, the 5,500 or so PSI pressure on the seal tends to downwardly-inwardly force or flow, or "pinch-off" the seal. And when that point in the valve life is reached that the case-hardened metal surfaces of the valve body and seat are worn away, the rate of metal wear becomes excessive, the clearance between the valve body and seat surfaces (at the aforesaid initial seal contact) increases, and the tendency to "pinch-off" becomes greater.
Further, when the "pinch-off" has progressed to a certain percentage of the sealing side, the rubber will distort and not seal off.
The "pinch-off" then, both shortens the life of the seal and renders the valve inoperative, in that the seal must seal off completely against any leakage of the abrasive fluid, which would of course cause the metal to cut out.
This invention uniquely relieves the foregoing sealing problem, as well as and in conjunction with its resolution also of the cushioning problem hereinbefore described.